Even though these authors demonstrated that SKI and SnoN expression in mela noma just isn’t linked with illness progression, they extrapolated, with out experimental proof, that SKI and SnoN may mediate the resistance of melanomas to development inhibition by TGF b. In our opinion, important and potentially dangerous concerns arise in the assumption that melanoma cells aren’t responsive to TGF b, at sophisticated stages of tumor progression, therapeutic inter ference with invasion and metastasis, two phenomena that do not demand cell proliferation and are largely below the control of TGF b, is likely to prove necessary. Targeting SKI, even though in some instance it may permit some reduction in tumor cell growth, as recommended by Medranos group, may perhaps just do the opposite, since it would do away with on the list of all-natural defenses that cells have created to interfere with autocrine TGF b sig nals.
Noteworthy, discrepancies regarding the capacity of TGF b to degrade SKI in melanoma cells have been sug gested to become on account of the concentrations selleck of TGF b made use of inside the many research, and that TGF b induced SKI degrada tion only occurs at non physiological concentrations. This can be not a satisfactory explanation as, if 1 follows this suggestion, increasing concentrations of TGF b would remove SKI and as a result exert its anti proliferative activity and inhibit tumor progression, in contradiction with experimental evidence that inhibition of TGF b signaling inhibits melanoma progression and metastasis. Note worthy, provided that TGF b blockade inhibits metastasis, then what ever active concentration is present is effective to promote metastasis in spite of doable higher levels of SKI expression.
Conclusions We supply evidence that despite high levels of c SKI oncoproteins in melanoma cells, TGF b sig naling is functional and contributes to melanoma cell invasiveness and metastasis. Exogenous TGF b induces a fast, proteasome mediated, degradation of c SKI, not accompanied by an inhibitory activity of TGF b on mel anoma cell proliferation. Though the original source understanding the exact part played by labile c SKI protein in melanoma remains to be understood, we think that targeting SKI to pre vent tumor spreading and disease progression is probably not an acceptable therapeutic tactic. Techniques Cells, plasmids and reagents Melanoma cell lines have already been described previously. NHEM were bought from Promocell and cultured in ready to use medium, also supplied by Promocell. All cells were grown at 37 C in a humidified atmosphere of 5% CO2. The reporter plas mids 9 MLP luc and 2. four kb p21 WAF1 promoter luciferase reporter construct were gifts from Drs. Sylviane Dennler and Bert Vogelstein, respectively. The pRL TK vector was from Promega. pSuper vector expressing SKI shRNA has been described previously.